This Application is also related to U.S. application Ser. No. 09/369,779 of Theodore Von Arx, filed Aug. 6, 1999, entitled xe2x80x9cElectrofusing of thermoplastic heating elements and elements made therebyxe2x80x9d; U.S. application Ser. No. 09/416,731 of John Schlesselman and Ronald Papenfuss, filed Oct. 13, 1999, entitled xe2x80x9cHeating element containing sewn resistance materialxe2x80x9d; U.S. application Ser. No. 09/275,161 of Theodore Von Arx, James Rutherford and Charles Eckman, filed Mar. 24, 1999, entitled xe2x80x9cHeating element suitable for preconditioning print mediaxe2x80x9d which is a continuation in part of U.S. application Ser. No. 08/767,156 filed on Dec. 16, 1996, now U.S. Pat. No. 5,930,459, issued on Jul. 27, 1999, which in turn is a continuation in part of U.S. application Ser. No. 365,920, filed Dec. 29, 1994, now U.S. Pat. No. 5,586,214, issued on Dec. 17, 1996; U.S. application Ser. No. 09/544,873 of Theodore Von Arx, Keith Laken, John Schlesselman, and Ronald Papenfuss, filed Apr. 7, 2000, entitled xe2x80x9cMolded assembly with heating element captured thereinxe2x80x9d; U.S. application Ser. No. 09/611,105 of Clifford D. Tweedy, Sarah J. Holthaus, Steven 0. Gullerud, and Theodore Von Arx, filed Jul. 6, 2000, entitled xe2x80x9cPolymeric heating elements containing laminated, reinforced structures and processes for manufacturing samexe2x80x9d; and U.S. application Ser. No. 09/309,429 of James M. Rutherford, filed May 11, 1999, entitled xe2x80x9cFibrous supported polymer encapsulated electrical componentxe2x80x9d which are all hereby incorporated by reference herein.
This invention relates to electrical resistance heating elements, and more particularly to formable thermoplastic laminate heated element assemblies.
It is known that polymers can be made electrically conductive by dispersing therein suitable amounts of finely divided conductive fillers, such as those comprising carbon black. Examples of such polymers may be found in U.S. Pat. No. 5,902,518 to Khazai et al., issued May 11, 1999 and in U.S. Pat. No. 4,388,607 to Toy et al., issued Jun. 14, 1983, the entirety of which are hereby incorporated by reference herein. Also, sheets of fibrous materials including conductive fibrous particles, such as carbon fibers, and having a pair of electrodes disposed on the surface of the sheets have been proposed as electrical heating units, such as is disclosed in U.S. Pat. No. 5,023,433 to Gordon, the entirety of which is incorporated by reference herein.
Still further, a heated container and a heated packaging for a product and method of manufacturing the same are described in Applicant""s co-pending application Ser. No. 09/642,215, herein incorporated in its entirety by reference. Several prior approaches to laminated heaters are also described in the application.
There still remains a need, however, for a heated container formed from a reformable but robust laminate electrical resistance heating element that effectively places the contents of the container in intimate contact with the heat source as well as a heated container that preferentially biases generated heat towards the product. There also remains a need for a heated container that provides for a more uniform heat distribution along the interior surface of the container. Still further, there remains a need for an economically manufactured and disposable container that is microwaveable while still providing the option of energizing the container to heat the contents therein.
The present invention provides a container comprising an electrically insulative and thermally conductive first polymeric layer, an electrically insulative and thermally insulative second polymeric layer, and a resistance heating layer laminated between the first and second polymeric layers to form a substantially continuous element structure. The resistance heating layer is coupled to a pair of electrical connectors. The substantially continuous element structure is formed into a final container structure having an interior and an exterior surface. The interior surface comprises the first polymeric layer and the exterior surface comprises the second polymeric layer.
The present invention as described above provides several benefits. A resistance heating layer is formed integral with the container, which places the contents of the container in intimate contact with the heat source, thereby providing for maximum use of the generated heat. The container can take on an infinite number of shapes and sizes, either open or closed, and even serve as the original packaging of a product, such as a food product. In that case, the product""s packaging may then be coupled to a power source, thereby heating the product while still in its original packaging. The continuous element structure may be thermoformed into a desired three dimensional heated plane, and known stamping or die cutting techniques may be used to cut the continuous element structure into reformable profiles. The heated element assembly thereby emulates well known sheet metal processing or known plastic forming processes and techniques. The continuous element structure is also robust enough to be included in injection, blow, vacuum, or compression molding processes to form a heated container or be over molded in a second molding step.
The above and other features of the present invention will be better understood from the following detailed description of the preferred embodiments of the invention which is provided in connection with the accompanying drawings.